Optimization of layup process for fabrication of wind turbine blades using model-based optical projection system

ABSTRACT

A method to design the kits and layup the reinforcement layers and core using projection system, comprising a mold having a contoured surface; a layup projection generator which: defines a plurality of mold sections; identifies the dimensions and location for a plurality of layup segments. A model-based calibration method for alignment of laser projection system is provided in which mold features are drawn digitally, incorporated into the plug(s) which form the wind turbine blade mold, and transferred into the mold. The mold also includes reflective targets which are keyed to the molded geometry wherein their position is calculated from the 3D model. This method ensures the precision level required from projection system to effectively assist with fabrication of wind turbine blades. In this method, digital location of reflectors is utilized to compensate for the mold deformations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of, and claims the benefit ofpriority under 35 U.S.C. § 120 to U.S. application Ser. No. 17/146,146filed on Jan. 11, 2021, which claims the benefit of priority under 35U.S.C. § 120 to U.S. application Ser. No. 16/023,891 filed Jun. 29,2018, which claims the benefit of priority under 35 U.S.C. § 119(e) ofU.S. Provisional Application No. 62/625,735 filed Feb. 2, 2018 and U.S.Provisional Application No. 62/527,726 filed Jun. 30, 2017, the entirecontents of each are hereby incorporated by reference.

THE FIELD OF THE DISCLOSED SUBJECT MATTER

The disclosed subject matter relates to a system for manufacturing windturbine blades. Particularly, the present disclosed subject matter isdirected to layup process of the wind turbine blade that corrects forreinforcement layers dislocation, core shifts or unwanted gaps tothereby preserve the structural integrity of the blade.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

The purpose and advantages of the disclosed subject matter will be setforth in and apparent from the description that follows, as well as willbe learned by practice of the disclosed subject matter. Additionaladvantages of the disclosed subject matter will be realized and attainedby the methods and systems particularly pointed out in the writtendescription and claims hereof, as well as from the appended drawings.

The sandwich composite structure of wind turbine blades allows forreaching the desired mechanical performance of the system while keepingthe weight of the blade minimal. In this arrangement, main structuralelements i.e. girders provide the load carrying capacity, reinforcementlayers form the aerodynamic surface of the blade and core material playsa critical role in supporting the skins from deformation and maintainingthe shape of the cross section. Consequently, layup process is asensitive and important step in fabrication of the wind turbine blade asany reinforcement layer dislocation, core shifts or unwanted gaps couldcompromise the structural integrity of the blade.

During the fabrication process and to facilitate the layup process aswell as transportation of material to the molds, reinforcement and corematerial is cut into smaller pieces known as “kitting”. Poor design ofkits leads to increased production cycle time and extends the risk ofcore gaps and quality issues as the in-mold tailoring and trimmingactivities will be increased.

In accordance with an aspect of the present disclosure, an optical (e.g.laser) projection system is provided that optimizes glass/core kittingprocess and facilitates manufacture of the blade. Optimized kittingpatterns not only address the quality concerns, but also shorten theproduction cycle time as well as the new product launch periodsignificantly.

The traditional method to kit the glass/core material is to use CADdrawings and 3D models of the blade to specify the edges and contoursand provide it to the suppliers to cut the parts. However, as CAD-basedkitting patterns deviate from actual parts in the mold, multipleiterations of kiting pattern revisions are required before the parts fitthe mold properly. Since there is no robust way of measuring the gapsand specifying the deviations under conventional techniques, thisiterative revision process is extremely time taking and tedious. Inaccordance with an aspect of the present disclosure, the manufacturingprocess utilizes an optical (e.g. laser) projection system to close thisloop, calibrate the 3D model and update the kitting pattern using theglass cuts and core panels' projection in the molds. Model-basedcalibration of projection system also ensures the desired level ofaccuracy in the process.

The accompanying drawings, which are incorporated in and constitute partof this specification, are included to illustrate and provide a furtherunderstanding of the method and system of the disclosed subject matter.Together with the description, the drawings serve to explain theprinciples of the disclosed subject matter.

In an exemplary embodiment of the present disclosure, a method forfabrication of a composite structure comprises receiving at least onespecification for a composite structure design, the composite structureincluding a plurality of core panels; generating a manufacturing modelof the composite structure design, the manufacturing model including aplurality of core panels; extracting at least one optical projectionfile from the manufacturing model, the optical projection file(s) havingcoordinates for projection of a marking(s) within a mold; identifyingselect reference features associated with a core panel; projecting atleast one marking to depict an edge of a core panel; and comparing corepanel reference features to the projected edge of the core panel.

At locations where the comparison of the core panel reference featuresand the projected edge of the core panel do not match, the methodadjusts the placement of the core panel, and/or adjusts themanufacturing model, which can include updating select core panelmeasurements.

The projecting can be performed by a plurality of overhead lasers thatare configured for relative movement with respect to the mold, and/orconfigured for relative movement with respect to each other.Additionally, the optical projection file(s) include edges of corepanels, and all core panel geometry is projected simultaneously or in aserial (i.e. one panel at a time) fashion. For purpose of illustration,the present disclosure can be embodied wherein the composite structureis a wind turbine blade including a root section and a tip section.

Additionally, the present disclosure includes a method for fabricationof a wind turbine blade comprising: receiving at least one specificationfor a blade design, the blade design including a plurality of corepanels; creating a mold, the mold configured for forming the blade andhaving a plurality of reflective targets included therein; generating a3D manufacturing model of the blade design, the manufacturing modelincluding a plurality of core panels; extracting at least one opticalprojection file from the manufacturing model, the optical projectionfile(s) having coordinates for projection of a marking(s) within a moldand digital coordinates for the reflective targets; calibrating anoptical projection apparatus; wherein calibration includes comparing theprojected marking to the digital location of the reflective target.

In an exemplary embodiment, the mold is created from a plug, the plugincluding reflective projector targets which are embedded into mold.Also, the projection apparatus includes a plurality of lasers, eachlaser aligned with six or more reflective targets. Additionally,adjacent laser projectors can be aligned with one or more sharedreflective targets.

In some embodiments, calibration of the optical projection apparatus isperformed at an elevated temperature, and the reflective targets (e.g.mirrors) are embedded within the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of various aspects, features, and embodiments ofthe subject matter described herein is provided with reference to theaccompanying drawings, which are briefly described below. The drawingsare illustrative and are not necessarily drawn to scale, with somecomponents and features being exaggerated for clarity. The drawingsillustrate various aspects and features of the present subject matterand may illustrate one or more embodiment(s) or example(s) of thepresent subject matter in whole or in part.

FIGS. 1-4 are schematic representations of a model-based Layup flowcharts in accordance with the disclosed subject matter.

FIG. 5 is an exemplary view of an overhead projection system disposedabove a blade mold.

FIGS. 6-11 are exemplary views of layup segments with laser projectionlines in accordance with the disclosed subject matter.

FIGS. 12-14 are exemplary views of a model-based calibration techniquein accordance with the disclosed subject matter.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Reference will now be made in detail to exemplary embodiments of thedisclosed subject matter, an example of which is illustrated in theaccompanying drawings. The method and corresponding steps of thedisclosed subject matter will be described in conjunction with thedetailed description of the system.

FIG. 1 depicts a blade model-based design/manufacturing process flowchart including the design input as well as the manufacturing outputsregarding the layup process. The calibrated manufacturing model asdescribed herein, could support an array of engineering disciplines(e.g. modelling, producibility-kitting, analysis) as well as productiondisciplines (e.g. glass layup, core placement, paste bead application).

The top section of FIG. 2 shows, in a traditional approach, the processbegins by generating the 3D model of a core inside the mold (step 0).Using this model, the flat pattern of the core (2D layout) is generated.The 2D layout is then virtually divided into several panels (step 1) andis provided to the kit supplier (step 2). The size and shapes of eachpanel can vary, with the maximum size of the panels being driven throughlogistic considerations (e.g. material handling). Following the firstcore placement trial during a new product launch, manual measurementtools are required to identify the deviations (including both design andmanufacturing related cases) and through several iterations (loop 1)between in-mold manual measurements and 2D drawing revisions, thekitting pattern is finalized.

In accordance with the disclosed method as shown in the bottom sectionof FIG. 2 , after flattening the 3D model and specifying the edges ofthe panel pieces (step 1′), the 2D kitting patterns are mapped back tothe 3D model (steps 0′). In some instances a plurality of edges arespecified for a given panel piece. For instance panel pieces which areinstalled within the root section can have a greater number of edgesspecified than panel pieces which are installed within the tip sectionof the blade. In some embodiments, all edges are specified whereas inother embodiments only select edges of a given panel piece arespecified. For instance, in regions of the mold in which the contour ischanging across panels, a greater number of edges can be specified toprovide a higher density mapping to accurately capture the gradient ofthe mold.

Using the updated model, the optical (e.g. laser) projection files areextracted (step 4). These projection files can be sent to all opticalprojectors, or in some embodiments only select projectors (e.g. rootprojection files sent to only those optical projectors which resideabove the root section of the mold/blade). Also, the projection filescan include a key (e.g. prefix or suffix, similar to addressing ofInternet Protocol packets) which signals that two particular projectionfiles are to be maintained in a consecutive manner as they are directedto adjacent panels within the mold.

During the core placement process on the shop floor (step 3), theprojected laser lines are used to identify the panels that are deviatingfrom the model. In some embodiments the identification of paneldeviation can be performed automatically (e.g. optical camera) withpredefined acceptable tolerance ranges. Additionally, or alternatively,the identification of panel deviation can be performed (or confirmed, ifinitially performed automatically) via manual inspection by theoperator. When a deviation beyond the acceptable limits is identified,the panel can be repositioned, or discarded, as desired. Also, an alertcan be signaled if/when a panel deviates beyond the acceptable toleranceto highlight this deviation. In some embodiments a confirmation that thedeviation has been addressed must be entered in order for a subsequentpattern to be projected.

Finalizing the core kitting pattern takes place through iterations (loop2) between laser-assisted in-mold measurements and 3D model. Theseiterations can be performed on a global approach, e.g. the entire loopis repeated, or only select sub-routines of the loop can be repeated, asdesired. Secondary to any modification attempts, the 3D model is updatedand both 2D patterns and laser projection files are revised accordingly.

These deviations are mainly due to the fact that 3D models are notcompletely representative of the actual geometry of the mold as well asthe glass and core layers. In addition, due to their porous structure,core materials may slightly deform before they are placed into themolds. One of the advantages of the disclosed method is the significantreduction in number of aforementioned iterations between loop 1 and 2.

The magnitude of acceptable error can depend on the materials employed,and the operating environment for a given blade. In some embodiments theacceptable error, or tolerance, can vary along and across the bladelocation. For example, the acceptable tolerance, or range deviation, canbe smaller at locations of material transition and/or thicknesstransitions, as well as along the leading and trailing edges.

FIG. 3 is a flowchart of a conventional layup design and executionapproach in which once the blade design (e.g. dimensions of length,chord, camber, etc.) is finalized, its specifications (1 and 2) aredetermined. From these input criteria, the manufacturing model isgenerated (3). This model is then used to design the glass cut and corekit (6), which can be a plurality of subsets which combine to form anaggregate to form the blade. These glass cuts and core kits (6) are thenapproved for production. During this stage quality check procedures andtools (9) are also generated. Upon delivery of the kits, the shopactivities begin. These activities include laying up glass pieces andcore panels in the mold (11). Once placed, their location is verifiedusing the quality check process (12). If approved, the core placementprocess is considered as complete. Often, however, discrepancies inposition are identified in the layup and the quality check processfails. Due to the open-loop structure, it is extremely difficult, if notimpossible, to determine root-cause-analysis of the discrepancy and makethe appropriate changes. Therefore, the troubleshooting stage is oftenlong and cumbersome. The techniques and corresponding apparatus of thepresently disclosed system is advantageous in that it addresses theshortcomings of the conventional approach, simplifies the complexity andshortens the duration of this stage by providing a closed-loopoptimization process.

FIG. 4 is a flowchart of a novel approach for optimization of blademanufacture using an optical projection system, as disclosed herein.Once a blade design (e.g. dimensions of length, chord, camber, etc.) isfinalized, its specifications (1 and 2) are determined. From these inputcriteria, the manufacturing model is generated (3). This model is thenused to extract laser projection files (4), as well as glass and corekit design (6). The projection files can include the edge locations ofeach panel/segment (e.g. entire perimeter of the panel/segment) to beplaced throughout the mold to form the composite structure, e.g. windturbine blade. Additionally, the projection files can include anindication of the center of origin used in calculating/determining theaforementioned edge locations.

After kit design is finalized, extra patterns can be added to theprojection files that specifically locate the features related to corepanel placement in the mold (e.g. distance from trailing edge, spar cap,etc.). These additional patterns can be based on the location, and/ortype of core structure/material within the mold. Some exemplary corematerials include end-grain balsa, styrene acrylonitrile (SAN) foam,polyvinyl chloride (PVC) foam and polyethylene terephthalate (PET) foam.In some embodiments, e.g., balsa and foam cores, the cores may be scoredor segmented to create hinges that allow it to conform to curvedsurfaces. This scoring can create gaps in the surface of the core whereone segment angles away from another. Accordingly, the additionalpatterns can be focused on these “problem” areas where there is a higherrisk/likelihood of gaps forming. Additionally or alternatively, therecan be a higher concentration of additional patterns located in thehigher load-bearing sections, e.g. root, than in the lower load-bearingsections of the blade.

Additionally, the optical projection system is installed and calibrated(5), as described in further detail herein, and the core kit design isforwarded to the supplier for production (8). Once the optical (e.g.laser) projection files and calibration steps are complete the shopactivity begins.

To provide design feedback all glass and core reference features definedby the quality check process (12) are tested against the laserprojection of glass and core reference features (10). If anydiscrepancies are observed at this stage, it is immediately concludedthat either the quality references or laser calibration should bereviewed and revised. In some embodiments, the manufacturing process canbe temporarily suspended until this review/revision is conducted. Insome embodiments, this review/revision can be performed can require anoperator/employee confirmation or approval.

Additionally, the present disclosure provides two separate qualitychecks to confirm accuracy of the panel placement. As shown in FIG. 4 ,there are two “match” diamonds presented in the flowchart, the upper“match” diamond compares the projected laser pattern and canrelay/update/correct discrepancies with the Laser Calibration File (5).Similarly, the lower “match” diamond compares the projected laserpattern with the core panel placement within the mold, and canrelay/update/correct discrepancies back to the core/glass panel design(6, 8)

Once approved, the glass and core is laid down using the laser patternas guidance using a method where a majority of pieces and panels areplaced based on a direct laser reference. In other words, each part ispositioned within the mold at a location in which its edge(s) is alignedwith the projected laser reference line. If a discrepancy occurs betweenthe projected geometry and the piece(s), the laser projectionsfacilitate isolation of individual parts and an enhanced categorizationof the discrepancy. This process provides sufficient information toquickly determine the root-cause-analysis which allows for accuratediagnosis of the problematic aspect of the manufacture (e.g. either thekit design or production).

Using this approach, the glass and core kitting and fitting processeshave a closed loop configuration (e.g. the highlighted items 3, 4, 6, 7,8, 10, 11 in FIG. 4 ) and troubleshooting process is significantlystreamlined.

FIG. 5 is an illustration of an exemplary embodiment of the opticalprojection system. In this exemplary embodiment a series of lasers (10)are positioned above the wind turbine mold and project patterns downwardonto the mold during the manufacturing process. The number of laserprojectors depends on the length of the blade as well as the height ofthe projectors with respect to the mold surface. The position ofprojectors in this exemplary embodiment are fixed but includeGalvo-driven mirrors built in each projector, such that laser beamreflections are moveable to create the 3D contours. While the lasersshown are independently mounted in a fixed position, alternativeconfigurations are contemplated in which all or a subset of laserprojectors are capable of relative movement with respect to each other.For example, a laser projector can adjust its vertical position withrespect to the blade mold, e.g. descend from the ceiling to bepositioned closer to the mold, so as to provide a more focused and vividpattern line of higher resolution. The projectors can be programmed withpredefined patterns for projection onto the blade mold (and/or any layupmaterials that may be disposed therein). Each blade design can require adistinct projection pattern, and thus a unique program inputted into theprojection system

EXAMPLES OF AN EXEMPLARY EMBODIMENT

The projected laser-assisted core kitting system disclosed herein wastested during the design and installation of a structural core of a windturbine blade. The core was designed in-house using a 3D model togenerate both a 2D flat pattern and 3D laser projections of the intendedpanel positions. The results of the projected laser-assisted corekitting system disclosed herein confirmed the benefits of providing thedata needed to perform a root-cause-analysis and closing the design loopwhen panels do not fit as expected. In many cases the installationmethod and traditional measurement techniques, rather than the coredesign, were found to be to be the root-cause of panel misfit and wereaddressed simply by having associates align the core to the laser lines.

Under the conventional process, measurements are taken either by handwith a tape measure and flexible ruler or with a FARO tracking laser.However, in a wind turbine mold setting, manual measurement with a metaltape measure is inaccurate along a curved surface and cannot account forthickness buildup from material already placed in the mold. Tapemeasures are also of limited use measuring angular deviations andpresent many opportunities for reading human error. Additionally, lasertracking with a FARO device is slow to collect data, is a limitedresource during a new product launch, and already has a tolerancestack-up (i.e. accumulation of multiple discrete variances) from thetooling. With limited options for data collection, engineering typicallychooses to simply adjust panel sizes based on how associates cut andpatch panels during installation without performing a root causeanalysis of the misfit. Failure to identify and fix underlying issuescreates problems when subsequent tooling lines are started and the coredoes not fit correctly in subsequent molds, driving further datacollection and changes.

Accordingly, the projected laser-assisted core kitting system disclosedherein was employed wherein the projections were created from the 3Dmodel as curves that outline the controlling locations. In thisexemplary embodiment, the edges along the blade leading edge, trailingedge, auxiliary spar cap pocket, and material transitions are modeledand projected into the blade mold. Additional reference lines can beprojected periodically, e.g., for every two to three panel edges, toserve as a visual confirmation that panels are being placed as modeled.

The modeling process of the present disclosure accounts for variousmaterial properties of the components used, e.g., the thickness of thedry glass, prefabricated parts, and consumables that are placed belowthe core, locating the boundaries and transitions more accurately thanany previous measurement methods. Accuracy is further improved over theconventional approach by using a local alignment method that eliminatestolerance stack-up from the tooling and corrects for mold expansion atelevated temperatures. In accordance with an aspect of the opticalprojection system disclosed herein, all core geometry can be projectedat once, providing engineering with an instantaneous visual evaluationof the core fitment. Additionally or alternatively, select regions (e.g.root vs. tip) can be projected in isolation, e.g. in a serial fashion,and/or for different durations. For example, the tip section may havethe edges projected for a longer time than the root section edges.

The implementation of the optical projection system disclosed herein,provides myriad of advantages over the conventional technique. Forexample, the system and method disclosed herein:

-   -   1) Aids discovery of root-cause of poorly fitting panels;    -   2) Provides an in-process check on other measurement methods        (previously not available, would require cutting blade to permit        inspection);    -   3) Permits rapid visual identification of panels cut incorrectly        by supplier in lieu of a time consuming incoming inspection;    -   4) Reduces measurement mistakes by the production team which        would otherwise cause delays when found by quality.    -   5) Shows angular misalignment caused by complex curvature.    -   6) Reduces noise in panel fit data, enabling a quicker revision        process.    -   7) Provides consistent panel placement by projecting reference        edges to reduce tolerance stack-up. This eliminates the need to        always start in the same location, granting more flexibility to        the production team; and minimizes waste by eliminating the need        for extra material stock typically required.

During conventional blade manufacture, any misfit in the core wasattributed to the design and production of the core panels, and the coredrawings would be adjusted to suite. The use of current disclosure nowintroduces a visible third datum, which often aligned with either thecore or the incumbent reference. In the case were the laser projectionsmatched a marked line, the core was quickly determined to be designed orcut incorrectly, in line with our incumbent process. Examples includethe supplier missing notes from the drawing, or a detail being missed inthe design.

In the case where the core matched the laser projection, but disagreedwith other measurement methods, further investigations were made. Themeasurement techniques and outcomes are discussed below.

Under the convention approach, the first two blades required 26supplemental panels taken from other core kits to fill gaps. Incontrast, only two panels were required for the third blade when thelaser projection system disclosed herein was employed, demonstratingthat an accurate installation method is as important as an accuratedesign. The following additional root causes of core misfit wereidentified through the use of presently disclosed projection lasersystem:

-   -   Spar cap location was found to be out of tolerance when the        prefab was placed on the layer of CFM that was positioned by        laser projector. (See FIGS. 6, 10 and 11 depicting spar cap        misalignment identified by laser projection). On the pressure        side it was previously ignored because it was in tolerance at        +/−5 mm, but the effect on core design is significant since the        placed tolerance is only +/−10 mm in the chord direction. Where        the core would have been adjusted under the conventional        technique, it can now be left unchanged to fit a nominal spar        cap position. On the suction side of the blade it had simply        been missed, under the conventional technique, that the spar cap        was out 18 mm at the root. Both pressure and suction side spar        cap positions can now be readjusted closer to nominal by        employing the laser projection system disclosed herein.    -   Auxiliary spar cap placement fixtures were located using the        conventional FARO tracker but did not align with the laser        projections of the present disclosure. Due to mold shrinkage,        that the FARO does not correct for, and an incorrect assumption        about design by the tracking team, the fixtures were positioned        out of tolerance. The core fit well when placed according to the        laser line without the fixtures, as disclosed herein.    -   The leading edge offset to the core was marked incorrectly by        quality review under the conventional technique. Making a        straight line measurement with a tape measure that does not        conform to mold surface, failure to correct for the difference        between aero edge and tool edge, failure to account for material        thickness, and making a wide marker line past the end of the        tape measure altogether produced a marked line that was 15 mm        too far into the blade. (See FIG. 7 depicting improper technique        in conventional manual measurements). Associates then cut the        core 20 mm shorter so the full marker line would be visible when        the core was placed, rather than targeting nominal. Without the        laser projections as disclosed herein, the core would have been        redrawn 20 mm shorter to match. Accordingly, implementation of        the current laser projection system resulted in no change being        needed.    -   Along the trailing edge the laser and manual markings were        initially matching due to the flatter curvature. Over the course        of installation a 10 mm deviation was observed between the laser        and the marked line. After re-measuring quality determined that        the TEUD prefab had slid 10 mm into the blade away from the        trailing edge, taking the marker line with it.    -   The panels were designed to sit square against the spar cap,        which is angled slightly from chordwise. Without lasers the team        fit the panels to a chordwise line, causing gaps and        interferences in the fit. When placed according to the lasers        the core fit well. The use of the lasers eliminated a need for        extra training, documentation, or specific product knowledge.        (See FIG. 8 depicting chordwise lines).    -   Complex curvature on the suction side in the transition from        round to max chord caused an angular deviation. Projection of        panel edge lines allowed fast visual identification of the        specific area that deviated so the sources of the error could be        identified and fixed. The conventional process would have made        the changes at the next transition, leaving as many as a dozen        panels misaligned from the intended position. (See FIG. 9        depicting manual measurement inaccuracies over TEUD due to        thickness buildup; laser projections match core position).

Accordingly, the projections of all core geometry identified errorsearly in the installation process. The location in the spanwisedirection between panels is defined as the top of the chamfer intransitions between two panels. This can be mistaken in production forthe edge of the panel. Unlike marker lines that can get covered as soonas core is put down, the laser line continues to show on top of the coreand allows an observer to see and point out a mistake. Following thetraditional method, quality would check the position, but only aftermany neighboring panels had been installed. The projected laser systemdisclosed herein also protects against situations where erroneousmarkings are made in the spanwise location to indicate where to beginlaying panels, and allow for the mistake to be quickly recognized andcorrected.

In summary, the conventional technique for the installation of core onblades required 26 extra supplemental core panels to fill gaps. Incontrast, with laser-assisted core installation disclosed herein, onlytwo panels were needed. This demonstrates that without lasers even awell-designed kit may appear not to fit, and that accurate placement ofeach individual panel can reduce the number of field changes required tomake a core kit meet tolerance. Additionally, projection lasers are acrucial tool in understanding the root causes of tolerance stack-up, andprovide a fast and efficient path towards a production-ready core kit.

Therefore, and in accordance with the disclosed subject matter, theoptimization method disclosed herein eliminates the need for manualmeasurement and open-loop kit revision which significantly lowers thenumber of required iterations and the final pattern fits with higherlevels of precision. Further, the disclosed optimization method allowsfor continued manual operator measurement to confirm tolerances arewithin acceptable ranges, if so desired.

Model-Based Calibration

In accordance with another aspect of the disclosure, a model-basedcalibration technique is disclosed for calibrating the projectionapparatus, e.g. plurality of Galvo-driven laser projectors.

FIGS. 12-14 schematically show the distortion of the mold surface inproduction space (FIG. 12-14 —in the lower half of the figurerepresented by the “(b) Shop Floor” label) relative to the plug geometry(FIG. 12-14 —in the upper half of the figure represented by “(a)Computer)” in digital space. This deformation could be caused by thermalloads or any other disturbing forces applied during mold production andservice. While original plug geometry (from which the mold for creatingthe wind turbine blade is created) and distorted geometry are identicalin all three figures, projection patterns are unique to the alignmentmethodology that is implemented in each case.

The traditional projection alignment method is depicted in FIG. 12 . Inthis approach, coinciding the coordinate system origins for bothproduction (“(b) Shop Floor” label) and digital (“(a) Computer”) spacesnear the root of the mold, position of the markers in the productionspace as described in the universal coordinate system is used (100) toalign the projection system. Following this method, the differencebetween the position of geometric features pre and post deformationleads to deviation between the laser projection space and productionspace. In the case of thermal shrinkage, as the deviations are stackingup starting from the origin of the coordinate system (00), error betweeneach feature and its associated projected pattern is increasing fromroot to the tip (Y>X). As the structure is tapered and non-homogeneous,the change in the deviations are not linear (Y 2X).

To improve the large stacked up error at the tip region, one solutionwould be to shift the origin of the coordinate system (00′) toward themiddle of the tooling as shown in FIG. 13 . In this scenario, althoughthe alignment method is identical to the previous case (using the actualmarker positions to for alignment purposes) the summation of deviationsbetween geometric features and their projected patterns is reduced. Inaddition, since the origin of the coordinate system is in the center ofgeometry, deviations are spreading toward tip and root sections in apseudo-symmetric manner (not completely symmetric as mentioned inprevious section X′) (′) and the maximum deviation around tip and rootare less than previous case (X′<Y and Y′<Y).

The process disclosed herein provides a methodology that eliminates thedeviations between projection and production spaces as shown in FIG. 14. In this arrangement, detected position of the markers in universalcoordinate system as installed on the tooling (FIG. 14 , “(b) ShopFloor”) is mapped to their equivalent mating feature in the digitalspace (100′). Full mapping of production space into the digital spaceautomatically result in a precise match between the projection space andproduction space in the shop floor. In other words, proposed mappingapproach, distorts the projection space to match the actual productionspace on the shop floor. Therefore, any kind of deformations on thetooling could be compensated this method. In addition, this approach isnot sensitive to the location of the coordinate system origin.

To execute this method, during the calibration process, instead of usingthe actual location of markers, the equivalent digital position of themis fed to the laser system as the reference points.

Local position tolerance, generally on the order of millimeters, iscritical for the relative position of different layers of material toeach other and to other features (e.g. leading edge). Global positiontolerance, defined as the position of a component at one end of the partrelative to the other end of the part, can be a full order of magnitudelarger than the local position tolerance. This larger global tolerancefacilitates cost savings that are vital to creating a competitiveproduct but increase the difficulty of achieving high local positiontolerances. Any replacement measurement technique must conform to bothof these accuracy regimes and maintain a continuous reference.

For embodiments in which a laser projection system is installed andcalibrated using a single global coordinate system, the extremities ofthe mold are likely to see local deviations equivalent to the globaldeformation of the tooling. Location of the target points may then betuned manually to reduce the observed variation between mold andprojection. This method however is unreliable and will require changeson the order of the global deformation, which invalidates thetraceability of this positioning back to the digital model.Additionally, this method must be performed at the same temperature usedto qualify the tooling, or it will be subject to deviations from thermalexpansion.

Local accuracy can be achieved without requiring high global accuracy byusing an array of projection lasers, each with its own local coordinatesystem. Each laser aligns to its own local targets, creating a localbest fit coordinate system. In this way the laser may achieve thehighest local accuracy possible. Adjacent lasers can be aligned usingone or more shared targets. If a global deformation is present, twoadjacent lasers can be aligned to different coordinate systems but havea minimal discontinuity at the projection boundary do to shared targetlocations. This approach permits large global deformations to berepresented as a series of small, permissible discontinuities in thearray.

In the case of unacceptably large discontinuities between adjacentprojectors, two options are available for improvement of fit; either thenumber of shared projection targets may be increased, or the number ofprojectors may be increased such that the discontinuity between any twoproctors becomes a smaller percentage of the global deformation.

One source of the large discontinuity is the effect of thermal expansionwhen the tool is heated. Molds are generally qualified at roomtemperature but are used in a heated state, where thermal expansion canbe greater than the allowable position tolerance. The present disclosureprovides an approach for aligning laser projectors that can be performedat any temperature since the reflector targets are referenced directlyoff the tooling itself such that the position of the references scaleswith the tool as is expands and contracts thermally. Since a roomtemperature mold is not required, alignment and calibration may beperformed concurrent with thermal testing or production. Through thesame mechanism the alignment.

In an exemplary embodiment, demonstration or validation of alignment ofthe projection array occurs before the system can be employed for use ina controlled manufacturing environment. The verification follows asimilar process as the alignment; projecting on top of known featuresthat have been transferred from the mold plug into/onto the mold, andtrace directly back to the 3D model. Any visually identifiable moldmarking may be used, such as mold scribe marks, insert geometries and/orsharp edges. Because these markings are transferred from a CNC cut plug,they provide the same benefits as previously discussed for the alignmentof the lasers. The accuracy of the aligned system is then considered tobe the maximum distance between a molded geometry and its associatedprojection. This measurement is small so may it be accurately made withmanual techniques such as the use of calipers, tape measure, ruler, etc.

While the disclosed subject matter is described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat various modifications and improvements may be made to the disclosedsubject matter without departing from the scope thereof. Moreover,although individual features of one embodiment of the disclosed subjectmatter may be discussed herein or shown in the drawings of the oneembodiment and not in other embodiments, it should be apparent thatindividual features of one embodiment may be combined with one or morefeatures of another embodiment or features from a plurality ofembodiments.

The invention claimed is:
 1. A method for fabrication of a compositestructure comprising: receiving at least one specification for acomposite structure design wherein the composite structure is a windturbine blade including a root section and a tip section, the compositestructure including a root portion having core panels and a tip portionhaving core panels to be located at a tip portion; generating amanufacturing model of the composite structure design, the manufacturingmodel including the root portion of core panels and the tip portion ofcore panels; extracting at least one optical projection file from themanufacturing model, wherein the optical projection file(s) includeedges of the root and the tip core panels; extracting a calibrationfile; placing the root portion of core panels and the tip portion ofcore panels within the mold; identifying a first portion of referencefeatures associated with the root portion of core panels and a secondportion of references features associated with the tip portion of corepanels, wherein the first portion of reference features are greater thanthe second portion of reference features, projecting at least onemarking to depict an edge of the root portion of core panels or the tipportion of core panels; and comparing core panel reference features tothe at least one marking depicting the edge; performing a quality checkof the at least one marking projected in accordance with the extractedoptical projection file.
 2. The method of claim 1, when the comparisonof the core panel reference features and the projected edge of the corepanel do not match, adjusting the placement of the core panel.
 3. Themethod of claim 1, when the comparison of the core panel referencefeatures and the projected edge of the core panel do not match,adjusting the manufacturing model.
 4. The method of claim 3, whereinadjusting the manufacturing model includes updating select core panelmeasurements.
 5. The method of claim 1, wherein projecting is performedby a plurality of lasers.
 6. The method of claim 5, wherein the lasersare configured for relative movement with respect to the mold.
 7. Themethod of claim 5, wherein the lasers are configured for relativemovement with respect to each other.
 8. The method of claim 1, whereinall core panel geometry is projected simultaneously.
 9. The method ofclaim 1, wherein select core panel markings are projected in a serialfashion.
 10. The method of claim 1, wherein projecting at least onemarking includes projecting from a plurality of lasers, each laseraligned with six or more reflective targets.
 11. The method of claim 1,wherein projecting at least one marking includes projecting from aplurality of lasers, adjacent laser projectors aligned with one or moreshared reflective targets.
 12. The method of claim 1, wherein projectingat least one marking includes projecting from a plurality of lasers, thelasers configured for relative movement with respect to the mold. 13.The method of claim 1, wherein projecting at least one marking includesprojecting from a plurality of lasers, the lasers configured forrelative movement with respect to each other.
 14. The method of claim 1,wherein reflective targets are embedded within the mold.
 15. The methodof claim 1, wherein the root core panels have a greater number of edgesspecified than tip core panels.
 16. The method of claim 1, wherein agreater number of edges are specified for root core panels and tip corepanels having a contour changing across two proximate panels.
 17. Themethod of claim 1, wherein the at least one optical projection filecomprises a root optical projection file and a tip optical projectionfile.
 18. The method of claim 17, wherein projecting the at leastoptical projection file comprises projecting via at least a rootprojector and at least a tip projector.
 19. The method of claim 18,wherein the at least a root projector projects the root opticalprojection file over the root core panels.
 20. The method of claim 18,wherein the at least a tip projector projects the tip optical projectionfile over the tip core panels.